6,396 research outputs found
Shear-free Null Quasi-Spherical Spacetimes
The residual gauge freedom within the null quasi-spherical coordinate
condition is studied, for spacetimes admitting an expanding, shear-free null
foliation. The freedom consists of a boost and rotation at each coordinate
sphere, corresponding to a specification of inertial frame at each sphere.
Explicit formulae involving arbitrary functions of two variables are obtained
for the accelerated Minkowski, Schwarzschild, and Robinson-Trautman spacetimes.
These examples will be useful as test metrics in numerical relativity.Comment: 20 pages, revte
On a Classical, Geometric Origin of Magnetic Moments, Spin-Angular Momentum and the Dirac Gyromagnetic Ratio
By treating the real Maxwell Field and real linearized Einstein equations as
being imbedded in complex Minkowski space, one can interpret magnetic moments
and spin-angular momentum as arising from a charge and mass monopole source
moving along a complex world line in the complex Minkowski space. In the
circumstances where the complex center of mass world-line coincides with the
complex center of charge world-line, the gyromagnetic ratio is that of the
Dirac electron.Comment: 17 page
Investigating reciprocity failure in 1.7-micron cut-off HgCdTe detectors
Flux dependent non-linearity (reciprocity failure) in HgCdTe NIR detectors
with 1.7 micron cut-off was investigated. A dedicated test station was designed
and built to measure reciprocity failure over the full dynamic range of near
infrared detectors. For flux levels between 1 and 100,000 photons/sec a
limiting sensitivity to reciprocity failure of 0.3%/decade was achieved. First
measurements on several engineering grade 1.7 micron cut-off HgCdTe detectors
show a wide range of reciprocity failure, from less than 0.5%/decade to about
10%/decade. For at least two of the tested detectors, significant spatial
variation in the effect was observed. No indication for wavelength dependency
was found. The origin of reciprocity failure is currently not well understood.
In this paper we present details of our experimental set-up and show the
results of measurements for several detectors.Comment: 11 pages, 10 figures, to appear in " Astronomical Telescopes and
Instrumentation: High Energy, Optical, and Infrared Detectors for Astronomy
IV", Proceedings of SPIE Vol. 774
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